If you use mod_security with your Apache server. It is necessary to have this configuration:
<VirtualHost *:443>
ServerName <ELABFTW_SUBDOMAIN>
<TLS PARAMETERS...>
# Disable outbound anomaly score
SecRuleRemoveById 959100
# Special config for /api endpoint
<Location /api >
SecRequestBodyAccess Off
SecRuleRemoveById 949110
</Location>
</VirtualHost>
List of rules is available here: https://www.netnea.com/cms/core-rule-set-inventory/
Please note that this is not a full-fledged configuration but rather a tweak that allows eLabFTW to work.