Error in writing to Relationship Classes “Failed to retrieve origin row for a relationship feature with OBJECTID '226' from table/feature class 'ARSiteVision_Images'

@rawansaleh The article Writing Geodatabase Relationship Classes is a little clearer. There is also an article specifically on attachments: Writing ArcGIS Geodatabase Attachments (although this deals with 1:M attachments so it's a little more complex)

In summary, you need to have the following attributes set on the different feature classes:

Origin:

• geodb_oid (this will be the same value as geodb_rel_origin_oid)
• geodb_feature_has_relationships = yes

Destination (_ATTACH)

• geodb_oid (this will be the same value as geodb_rel_destination_oid)
• geodb_feature_has_relationships = yes

Relationship (_ATTACHREL)

• geodb_rel_origin_oid (same as geodb_oid on origin)
• geodb_rel_destination_oid

• geodb_type = geodb_relationship or geodb_attributed_relationship

I think you might be renaming geodb_oid to geodb_rel_origin_oid before the 'origin' feature class. Use feature caching - you can then look at each feature before they enter the writer to ensure they have the correct attributes.