Root composer.json requires messente/messente-api-php ^1.4 -> satisfiable by messente/messente-api-php[1.4.0].
messente/messente-api-php 1.4.0 requires guzzlehttp/guzzle ^6.2 -> found guzzlehttp/guzzle[6.2.0, ..., 6.5.x-dev] but it conflicts with your root composer.json require (^7.0.1).