Spotify on iPhone cannot see Firestick in "Devices Available"

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Plan

Premium

Country

 UK

Device

iPhone 5S

Operating System

(iOS 12.1.4

My Question or Issue

 iPhone can no longer detect Firestick in "devices available", or at least it is intermittent. Have tried restarting phone and Firestick; other devices work can see it ok, including another iPhone. Was working fine until a couple of weeks ago. Any ideas would be appreciated thank you