In MariaDB the comments must be followeb by a space.

From a '-- ' to the end of a line. The space after the two dashes is required (as in MySQL).

Source: https://mariadb.com/kb/en/library/comment-syntax/

Please try ' OR 1=1 --[space]

In MariaDB the comments must be followed by a space:

From a '-- ' to the end of a line. The space after the two dashes is required (as in MySQL).

Please try ' OR 1=1 --[space].