Process model is unable to access a document when the form interface is using a a!startform and being called in the site

it apparently has no permissions, however it works when on interface, but it doesn't on the site. All permissions were conceded.

This error message in instance details only happens when using the site itself. But when using the interface it doesn't.

The S3 node simply doesn't access the document through the process model

Any thoughts on it? Thanks in advance

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