cannot copy unfinished logical replication slot “…”

Symptoms

A statement failed with SQLSTATE 0A000 (feature_not_supported), reported at severity ERROR. This is a Feature Not Supported condition: PostgreSQL emits the message cannot copy unfinished logical replication slot "…".

• The client receives SQLSTATE 0A000 (feature not supported).
• The operation is rejected at ERROR level; the statement does not complete.

What the server log shows

ERROR:  cannot copy unfinished logical replication slot "…"
HINT:  Retry when the source replication slot's confirmed_flush_lsn is valid.

Why PostgreSQL raises this

Class 0A (Feature Not Supported) means the statement was syntactically valid but asked for an operation this server does not implement, or that is not allowed in the current context.

As described in PostgreSQL’s Appendix A PostgreSQL Error Codes, SQLSTATE 0A000 carries the condition name feature_not_supported in class Feature Not Supported. (Paraphrased — see the linked reference for the exact wording.)

Common causes

• Using a SQL feature or option not implemented by this PostgreSQL version.
• Attempting an operation disallowed in the current context (e.g. inside a transaction block).
• Combining clauses that PostgreSQL does not support together.

How to fix it

1. Rewrite the statement to avoid the unsupported feature.
2. Check the version notes — the feature may exist in a newer release.
3. Move the operation outside the disallowed context if applicable.

Version applicability

This message is present in PostgreSQL 15, 16, 17, 18 and 19.

Related & next steps

• SQLSTATE 0A000 — Feature Not Supported (full reference)
• PostgreSQL error code index

Reference: PostgreSQL Appendix A PostgreSQL Error Codes.