Fragment identifier is not defined EPUB error

I know this error has been posted before but I'm at my wit's end with this and I can't seem to resolve it through the previous post's advice.

This is the error:

Can anybody please help me?

I'm uploading an EPUB 3.0 to IngramSpark. What do you need to know to help me?

Thanks so much for your time

Community Expert

What are your InDesign and operating system versions?

Participant

I'm using InDesign through Creative Cloud so it's 20.5.

Community Expert

i wonder if this helps:

...or this:

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