Unable to add testflight to build group

I have published my app to testflight and it is "ready to submit" , however when I am trying to add it to my external testing build group it keeps showing an error, so I am not really sure what is wrong with it. My previous build have no issues , but ever since I encountered this problem all my previous builds got expired too . Please help

Unable to add testflight to build group
 
 
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