Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires guzzlehttp/guzzle ^7.8 -> satisfiable by guzzlehttp/guzzle[7.15.1]. - guzzlehttp/guzzle 7.15.1 requires guzzlehttp/psr7 ^2.13 -> found guzzlehttp/psr7[2.13.0] but it conflicts with your root composer.json require (^3.0.0). Problem 2 - Root composer.json requires hosmelq/sse ^0.1.0 -> satisfiable by hosmelq/sse[v0.1.0]. - guzzlehttp/guzzle 7.15.1 requires guzzlehttp/psr7 ^2.13 -> found guzzlehttp/psr7[2.13.0] but it conflicts with your root composer.json require (^3.0.0). - hosmelq/sse v0.1.0 requires guzzlehttp/guzzle ^7.9 -> satisfiable by guzzlehttp/guzzle[7.15.1].