I can specify tangency for a Boundary Surface feature through the GUI, but not through the API (SW 2023).  The macro below creates a Boundary Surface feature using an edge and a sketch in direction 1, and two sketches in direction 2.  I use SetNetBlendCurveData to specify that the surface should be tangent to the adjacent surface at the edge, but it does not do anything.  The tangency condition shows as "None" in the feature editor.

Am I doing something wrong?

Dim swApp As SldWorks.SldWorks
Dim swModel As ModelDoc2
Dim swSketchMgr As SketchManager
Dim swFeatMgr As FeatureManager
Dim swSketchSegment As SketchSegment

Sub main()
    Set swApp = Application.SldWorks

    ' Create new part
    Set swModel = swApp.NewPart
    Set swSketchMgr = swModel.SketchManager
    Set swFeatMgr = swModel.FeatureManager

    ' Select Front Plane and create sketch
    swModel.Extension.SelectByID2 "Front Plane", "PLANE", 0, 0, 0, False, 0, Nothing, 0
    swSketchMgr.InsertSketch True

    ' Draw a rectangle (100mm x 50mm) bottom left at origin
    ' swSketchMgr.CreateCornerRectangle 0, 0, 0, 0.1, 0.05, 0

    Dim centerX As Double: centerX = 0.05      ' Midpoint of top edge
    Dim centerY As Double: centerY = 0.025     ' Center of rectangle
    Dim radius As Double: radius = 0.03
    Dim angle As Double: angle = 30 * (3.14159265359 / 180) ' 30 degrees in radians

    ' Start and end points of arc (60 degrees total)
    Dim startX As Double: startX = centerX + radius * Sin(angle)
    Dim startY As Double: startY = centerY + radius * Cos(angle)
    Dim endX As Double: endX = centerX + radius * Sin(-angle)
    Dim endY As Double: endY = centerY + radius * Cos(-angle)

    swSketchMgr.CreateArc centerX, centerY, 0, startX, startY, 0, endX, endY, 0, 1 ' Coouterclockwise arc

    ' Close the crescent shape with a line
    swSketchMgr.CreateLine endX, endY, 0, startX, startY, 0

    swSketchMgr.InsertSketch True
    
    swModel.ClearSelection2 True
    boolstatus = swModel.Extension.SelectByID2("Sketch1", "SKETCH", 5.87644585700619E-02, 0.050824615470025, -5.85795561566647E-04, False, 1, Nothing, 0)
    boolstatus = swModel.InsertPlanarRefSurface()
    swModel.ClearSelection2 True
    
    Dim swSurfFeat As Feature
    Dim swSurfBody As Body2
    Dim edges As Variant
    Dim crescentEdge As edge
    Dim i As Integer
    
    Set swSurfFeat = swModel.FeatureByPositionReverse(0)
    edges = swSurfFeat.IGetBody2().GetEdges
    For i = LBound(edges) To UBound(edges)
        Dim e As edge
        Set e = edges(i)
        Dim curve As curve
        Set curve = e.GetCurve()
        If curve.IsCircle Then
            Set crescentEdge = e
            Exit For
        End If
    Next

    ' === 3D Arcs Going Upward (YZ Plane) ===
    ' 1st sketch (arc 1)
    swSketchMgr.Insert3DSketch True
    
    Dim arc1Sketch As Feature
    Set arc1Sketch = swModel.FeatureByPositionReverse(0)

    Dim R As Double: R = 0.0025
    Dim arcAngleDeg3D As Double: arcAngleDeg3D = 90
    Dim arcAngleRad3D As Double: arcAngleRad3D = arcAngleDeg3D * (3.14159265359 / 180)

    ' Start 3D Arc (left end of crescent)
    Dim arc1 As SketchSegment
    Dim x1 As Double: x1 = startX
    Dim y1 As Double: y1 = startY
    Dim z1 As Double: z1 = 0
    Dim y1mid As Double: y1mid = y1 + R * Sin(arcAngleRad3D / 2)
    Dim z1mid As Double: z1mid = z1 + R * (1 - Cos(arcAngleRad3D / 2))
    Dim y1end As Double: y1end = y1 + R * Sin(arcAngleRad3D)
    Dim z1end As Double: z1end = z1 + R * (1 - Cos(arcAngleRad3D))

    Set arc1 = swSketchMgr.Create3PointArc(x1, y1, z1, x1, y1end, z1end, x1, y1mid, z1mid)
    
    swSketchMgr.Insert3DSketch False
    
    ' 2nd sketch (arc 2)
    swSketchMgr.Insert3DSketch True
    
    Dim arc2Sketch As Feature
    Set arc2Sketch = swModel.FeatureByPositionReverse(0)

    ' End 3D Arc (right end of crescent)
    Dim arc2 As SketchSegment
    Dim x2 As Double: x2 = endX
    Dim y2 As Double: y2 = endY
    Dim z2 As Double: z2 = 0
    Dim y2mid As Double: y2mid = y2 + R * Sin(arcAngleRad3D / 2)
    Dim z2mid As Double: z2mid = z2 + R * (1 - Cos(arcAngleRad3D / 2))
    Dim y2end As Double: y2end = y2 + R * Sin(arcAngleRad3D)
    Dim z2end As Double: z2end = z2 + R * (1 - Cos(arcAngleRad3D))

    Set arc2 = swSketchMgr.Create3PointArc(x2, y2, z2, x2, y2end, z2end, x2, y2mid, z2mid)
    
    swSketchMgr.Insert3DSketch False
    
    ' 3rd sketch (Connecting line between tops of arcs)
    swSketchMgr.Insert3DSketch True
    
    Dim lineSketch As Feature
    Set lineSketch = swModel.FeatureByPositionReverse(0)

    Dim line As SketchSegment
    Set line = swSketchMgr.CreateLine(x1, y1end, z1end, x2, y2end, z2end)

    swSketchMgr.Insert3DSketch False
    
    ' Select curves: direction 1: crescent arc (edge), connecting line
    '                direction 2: two 3D arcs

    swModel.ClearSelection2 True

    ' Select crescent edge
    Dim selDataCrescent As SelectData
    Set selDataCrescent = swModel.SelectionManager.CreateSelectData
    selDataCrescent.Mark = 8193
    boolstatus = crescentEdge.Select4(True, selDataCrescent)

    boolstatus = lineSketch.Select2(True, 16385)
    boolstatus = arc1Sketch.Select2(True, 12290)
    boolstatus = arc2Sketch.Select2(True, 24578)
    
    swFeatMgr.SetNetBlendCurveData 0, 0, 3, 0, 1, True  ' Make 1st curve of the first direction tangent to the adjacent face
    
    Dim blendFeature As Feature
    Set blendFeature = swFeatMgr.InsertNetBlend2(2, 2, 2, False, 1, False, True, True, True, False, -1, -1, False, -1, False, False, -1, False, -1, False, False)
    
End Sub

Thanks!