Failing installation

[acharseth]

When I try to Install with composer require laulamanapps/izettle-api I get error message:

  Problem 1
    - laulamanapps/izettle-api[dev-master, dev-InventoryClient, dev-releases/1.0-dev, dev-moneyphp-1.3-compatible, v0.9, ..., v0.9.4] require guzzlehttp/guzzle ^6.3 -> found guzzlehttp/guzzle[6.3.0, ..., 6.5.x-dev] but it conflicts with your root composer.json require (^7.2).
    - Root composer.json requires laulamanapps/izettle-api * -> satisfiable by laulamanapps/izettle-api[dev-InventoryClient, dev-master, dev-releases/1.0-dev, dev-moneyphp-1.3-compatible, v0.9, ..., v0.9.4].
...

Sorry if this is not a bug, but an installation issue, which chould not be issued here.