2201B: invalid_regular_expression

What does it mean?

The pattern given to a regular expression operation (~, ~*, SIMILAR TO, regexp_matches, substring etc.) is invalid. PostgreSQL could not compile the pattern because its syntax is wrong.

Why does it happen?

A regex pattern with unbalanced parentheses, invalid character classes, bad escape sequences or an unsupported construct. A common cause is using user input directly as a pattern without escaping its special characters.

How to fix it

Fix the regex pattern according to POSIX/ARE syntax; check parentheses, brackets and escape sequences. If you are searching for user input as literal text rather than as a pattern: PostgreSQL has no built-in regexp_quote function, so escape the special characters by prefixing them with a backslash via regexp_replace, or avoid regex entirely and use strpos()/position() or LIKE ... ESCAPE. Validate the pattern by testing it in a separate tool.