The availability of booking of trips in the mobile app is dependant upon the configuration of the contract to which the trip belongs.
To view the contract settings confirm the following:
View the trip you are interested in Trips>Trip Calendar>View Trip
Check the name of the contract
Go to view organisation>Contract
Select View for the relevant contract name
Confirm that the searchable by section has the correct configuration for the default rules, be aware that an override rule will superceed the default rules for a single route within the contract and may have different configurations, as a override rule will supersede a default rule in its entirety, notifications in addition to the searchable by are impacted, ensure you check these are as you expect as well