TypeError: Argument 2 [...] must be an instance of Drupal\metatag_import_export_csv\mixed, string given

Speaking with another developer ( Ghazlawl → ), they mentioned that the mixed type isn't available in PHP 7.

PHP.net states that the mixed type was not introduced until PHP 8.0.0.

This module lists support down to Drupal 9.3 and Drupal 9.x supports down to PHP 7.3 → .

Since mixed is not available in PHP 7, I've changed the variable type to be string since that's what the errors during testing mentioned as the variable type provided when uploading a CSV.

I've created a tiny patch to set the variable type to string, but it may need to be tested with other delimiters.

Ah, created the patch from an incorrect folder, fixed in new patch.