I had a similar error during a recent project where I was integrating Mailgun in Laravel. In my case the problem was not with Mailgun at all but overlooked PHP syntax errors around array definitions. I eventually discovered that the issue sometimes originates from misplaced commas or mistyped quote marks elsewhere in the file, causing PHP to misinterpret subsequent arrays. It helped to double-check the entire file for any syntax errors. After cleaning up the code and ensuring proper PHP syntax throughout, the system started working without any T_DOUBLE_ARROW unexpected error. Thorough debugging is always a key practice when untangling these issues.
I encountered a similar issue when integrating Mailgun with Laravel, and I found that the error was not directly caused by Mailgun but rather by a subtle PHP syntax mistake. In my case, verifying that all arrays and key-value pairs used consistent formatting helped identify the problem. I took the approach of reducing the file to a minimal example to isolate the error, and that revealed that a small typo elsewhere was affecting the configuration array. Meticulous review of the surrounding syntax often resolves such issues.
i had a simlar issue before - turns out a stray comma or mistyped quote somewhere earlier in the file was the real culprit. check your code right before the mailgun config, it might not be mailgun at all. good luck!