Error when changing the order status of an order

SyntaxError: JSON.parse: unexpected end of data at line 1 column 1 of the JSON data
parsererror

It’s a bug in OpenCart 3.0.3.9

To fix this bug, it is recommended to update opencart 3.0.3.9 to 3.0.4.0 or follow this to fix the bug https://github.com/opencart/opencart/commit/402559b4ad68624d6d6cd5c21e0f978aee3b07bd