Is the document actually in the connected mailbox?
Open the original message through a trusted route and check that it has a PDF attachment. A payment notice or portal link is not the PDF document itself. Check the mailbox, selected IMAP folders and search period.
Are the period and search completion correct?
The email receipt date can differ from the payment or invoice issue date. Deliberately widen the selected range if the message arrived outside it. Check whether processing completed, failed or paused because of plan volume.
Is the document waiting for a decision?
The document may be marked unclear, personal, not an invoice or a copy of a known invoice. Look at the relevant status and reason. For incorrect classification, correct the specific item, not all settings blindly.
If the cause is unclear
Give support the search identification, approximate time and expected-result description. Do not share passwords or the entire mailbox content. Do not delete all available documents as your first repair attempt; you would lose useful information about what succeeded.