Title slug 'echoes' is in use by series 'Echoes'.

Help & Support
1

Sonarr version (exact version): 4.0.14.2939
OS: Synology DSM7
Description of issue: Echoes (2022) cannot be added if Echoes (1988) is already present.

2

According to TheTVDB rules one of them should be renamed. Weird scenario where the newer series has existed longer than the original on TheTVDB.