@rajank11, No problem. There are a couple of “Gotchas” I found with the R-series. Unfortunately, I do not know if these apply to the HW-J7500 as I never used that. However, like I said, I do have a bunch of experience with the R1 & R3.
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Give the speaker a static IP via a DHCP reservation in your router. This is very important. It appears that there is something iffy with the integration with the Samsung MultiRoom speakers. Everytime the speaker gets a new IP (if left to standard DHCP), it shows up as a new speaker. Using the Samsung MultiRoom app, you can get the MAC address of the speaker, and then key it into your router with a DHCP reservation. This will ensure that the speaker always gets the same IP from DHCP, which will save you headaches in the long run.
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When looking at your speakers, chances are that you will see more speakers than you have (re: above). In my case, when I got my first R3 and attempted to pair it, it showed FOUR different samsung speakers. There are only two things that identify the correct speaker: The IP address (re: above) and the speaker status (paused vs stopped). You want to make sure you are selecting the speaker that reads “Stopped”. This is the correct and active speaker. All of the speakers that read “paused” on the list, in my experience, will never play audio.
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The samsung speaker has three modes, iirc. WiFi, Bluetooth, TV Bluetooth (or something like that). It is imperative that the R7 be on WiFi. The speaker essentially acts as a mini receiver. Think of each mode as an input because…well, they are. If you are using the R7 as a bluetooth speaker through your phone, you will never hear ST TTS come through. It doesn’t automatically switch inputs. The speaker must be in WiFi mode in order for it to output the audio from ST TTS. It’s very possible that everything is currently setup correctly on your end, but it’s just on the wrong input.
Because of #3, I wound up buying two speakers. an R1 for ST TTS and kept the R3 as a bluetooth speaker for my Echo Dot’s and other various devices. It appears that if you want Samsung MultiRoom speakers to always be available for ST TTS, you need to buy dedicated speakers for that purpose. They are not dynamic enough to switch inputs when an event occurs.
Again, these are my findings. They may not be the only way to skin the cat, but this is how I have set it up in the past and it is still working today. 
Hopefully this helps you! If you need anything else, just tag me in a post.
[EDIT] It is to also be noted that I am using BigTalker for all of my TTS; amazing app! I do not use the ‘Notify with Sound’ SA. I can also confirm that TTS is working on this end. Everything seemed to be back in order once the support team sent out the “All clear” message.
[EDIT2] Tagging @sam_alian because the first three pieces may help him as well.