How does the EPO provide notification of the standardised sequence listing in TXT or XML format that is part of the application documents intended for grant (communication under Rule 71(3) EPC)?

If you have activated Mailbox, a sequence listing forming part of the description in TXT format or XML format is included as a ZIP file in the communication under Rule 71(3) EPC. If you have not activated Mailbox, a link (URL address) to download the sequence listing in TXT or XML format from a safe repository linked to the European Patent Register is included in the communication under Rule 71(3) EPC.  

For more details, see OJ EPO 2021, A97, points 37 and 41, and New standard for sequence listings now visible to users.