Composer Fatal error: Declaration of Fxp... must be compatible with ...AbstractAssetsRepository.php on line 334

You can temporarily disable composer plugins with the --no-plugins option:

composer global remove fxp/composer-asset-plugin --no-plugins

See Composer docs - Global options:

--no-plugins: Disables plugins.

To solve the above error while installing composer asset plugin please do the following

1. delete fxp folder in the path C:\Users\UserName\AppData\Roaming\Composer\vendor

2. remove "fxp/composer-asset-plugin": "^1.4" from composer.json file in composer folder

3. run this command composer global remove fxp/composer-asset-plugin --no-plugins to make sure no fxp folder is left and json data

4. composer global require fxp/composer-asset-plugin --no-plugins Run this command to install composer asset plugin and it will be installed easily

5. If you want to update existing plugin, run this command

   composer global update fxp/composer-asset-plugin --no-plugins