But "open source to those who pay" is quite a stretch of the definition.
If you check Open Source Initiative's list of approved licenses, you won't find anything that fits this definition:
https://opensource.org/licenses
The closest I know to what you're describing is Business Source License (BSL):
https://en.wikipedia.org/wiki/Business_Source_License
> The Business Source License (SPDX id BUSL) is a software license which publishes source code but limits the right to use the software to certain classes of users. The BUSL is not an open-source license, but it is source-available license that also mandates an eventual transition to an open-source license. This characteristic has been described as a compromise between traditional proprietary licenses and open source.