please help, magento 2.2.6 to 2.3 upgrade fails with composer

[megenboy_dunee]

I tried to upgrade my 2.2.6 Magento install with composer following the tutorial on Magento Website, but "composer update" fails with these errors below:

Spoiler

Problem 1
- magento/inventory-composer-installer 1.0.3 requires composer-plugin-api ^1.1 -> no matching package found.
- magento/product-community-edition 2.3.0 requires magento/inventory-composer-metapackage ^1.0.3 -> satisfiable by magento/inventory-composer-metapackage[1.0.3].
- magento/inventory-composer-metapackage 1.0.3 requires magento/inventory-composer-installer ^1.0.3 -> satisfiable by magento/inventory-composer-installer[1.0.3].
- Installation request for magento/product-community-edition 2.3.0 -> satisfiable by magento/product-community-edition[2.3.0].

Potential causes:
- A typo in the package name
- The package is not available in a stable-enough version according to your minimum-stability setting
see <https://getcomposer.org/doc/04-schema.md#minimum-stability> for more details.

[n0kit31]

Try to remove vendor directory and re-hit the command.

[Manthan Dave]

Hi @megenboy_dunee 

Looking at the error it sees like package is are not compatible with your PHP version.

Which PHP version are you using ?