~/bin/phpbrew known --update         

Downloading https://www.php.net/releases/index.php?json=1&version=8&max=100 via curl extension
Downloading https://www.php.net/releases/index.php?json=1&version=7&max=100 via curl extension
8.4: 8.4.2, 8.4.1 ...
8.3: 8.3.15, 8.3.14, 8.3.13, 8.3.12, 8.3.11, 8.3.10, 8.3.9, 8.3.8 ...
8.2: 8.2.27, 8.2.26, 8.2.25, 8.2.24, 8.2.23, 8.2.22, 8.2.21, 8.2.20 ...
8.1: 8.1.31, 8.1.30, 8.1.29, 8.1.28, 8.1.27, 8.1.26, 8.1.25, 8.1.24 ...
8.0: 8.0.30, 8.0.29, 8.0.28, 8.0.27, 8.0.26, 8.0.25, 8.0.24, 8.0.23 ...
7.4: 7.4.33, 7.4.32, 7.4.30, 7.4.29, 7.4.28, 7.4.27, 7.4.26, 7.4.25 ...
7.3: 7.3.33, 7.3.32, 7.3.31, 7.3.30, 7.3.29, 7.3.28, 7.3.27, 7.3.26 ...
7.2: 7.2.34, 7.2.33, 7.2.32, 7.2.31, 7.2.30, 7.2.29, 7.2.28, 7.2.27 ...
7.1: 7.1.33, 7.1.32, 7.1.31, 7.1.30, 7.1.29, 7.1.28, 7.1.27, 7.1.26 ...
7.0: 7.0.33, 7.0.32 ...

...
5.6: 5.6.17 ....

phpbrew install php-5.6

Exception: Version 5.6 not found.