Unity Plugin related problem linking app on iOS

Solar2D Monetization (in-app purchases, ads, etc.)
#1

Build is failing with:-

ld: framework not found IronSource
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
BUILD ERROR: There was a problem linking the app.

Have narrowed it down to plugin.unityads.v4.

Have tried build 3711 and 3727.

Have built multiple apps and have the same issue. This was working a week ago with the same build and code, so something must have changed on the back end / plugin.

Please resolve quickly as this is blocking a release.

Thanks!