Hi Abdiel,
When you try to generate in IOS with MABS 6.3/7.0 there are 4 errors:
[VERBOSE] [Build] /var/lib/builder02/builds/58ed0d18-7a43-47c2-95a9-b7683540f752/source/platforms/ios/TextToSpeechDemo/Plugins/cordova-plugin-tts/CDVTTS.m:64:19: error: redefinition of 'options'
[VERBOSE] [Build] NSDictionary* options = [command.arguments objectAtIndex:0];
[VERBOSE] [Build] ^
[VERBOSE] [Build] /var/lib/builder02/builds/58ed0d18-7a43-47c2-95a9-b7683540f752/source/platforms/ios/TextToSpeechDemo/Plugins/cordova-plugin-tts/CDVTTS.m:40:19: note: previous definition is here
[VERBOSE] [Build] NSDictionary* options = [command.arguments objectAtIndex:0];
[VERBOSE] [Build] ^
[VERBOSE] [Build] /var/lib/builder02/builds/58ed0d18-7a43-47c2-95a9-b7683540f752/source/platforms/ios/TextToSpeechDemo/Plugins/cordova-plugin-tts/CDVTTS.m:66:15: error: redefinition of 'text'
[VERBOSE] [Build] NSString* text = [options objectForKey:@"text"];
[VERBOSE] [Build] ^
[VERBOSE] [Build] /var/lib/builder02/builds/58ed0d18-7a43-47c2-95a9-b7683540f752/source/platforms/ios/TextToSpeechDemo/Plugins/cordova-plugin-tts/CDVTTS.m:42:15: note: previous definition is here
[VERBOSE] [Build] NSString* text = [options objectForKey:@"text"];
[VERBOSE] [Build] ^
[VERBOSE] [Build] /var/lib/builder02/builds/58ed0d18-7a43-47c2-95a9-b7683540f752/source/platforms/ios/TextToSpeechDemo/Plugins/cordova-plugin-tts/CDVTTS.m:67:15: error: redefinition of 'locale'
[VERBOSE] [Build] NSString* locale = [options objectForKey:@"locale"];
[VERBOSE] [Build] ^
[VERBOSE] [Build] /var/lib/builder02/builds/58ed0d18-7a43-47c2-95a9-b7683540f752/source/platforms/ios/TextToSpeechDemo/Plugins/cordova-plugin-tts/CDVTTS.m:43:15: note
[VERBOSE] [Build] : previous definition is here
[VERBOSE] [Build] NSString* locale = [options objectForKey:@"locale"];
[VERBOSE] [Build] ^
[VERBOSE] [Build] /var/lib/builder02/builds/58ed0d18-7a43-47c2-95a9-b7683540f752/source/platforms/ios/TextToSpeechDemo/Plugins/cordova-plugin-tts/CDVTTS.m:68:12: error: redefinition of 'rate'
[VERBOSE] [Build] double rate = [[options objectForKey:@"rate"] doubleValue];
[VERBOSE] [Build] ^
[VERBOSE] [Build] /var/lib/builder02/builds/58ed0d18-7a43-47c2-95a9-b7683540f752/source/platforms/ios/TextToSpeechDemo/Plugins/cordova-plugin-tts/CDVTTS.m:44:
[VERBOSE] [Build] 12: note:
[VERBOSE] [Build] previous definition is here
[VERBOSE] [Build] double rate = [[options objectForKey:@"rate"] doubleValue];
[VERBOSE] [Build] ^
[VERBOSE] [Build] 4 errors generated.
This plugin uses https://github.com/LuisMAlmeida/cordova-plugin-tts (version forked from https://github.com/vilic/cordova-plugin-tts). These versions in the IOS source (src/ios/CDVTTS.m) have a redefinition of variables problem that does not allow to compile in IOS.

Options
- You can wait a fix in cordova plugin https://github.com/LuisMAlmeida/cordova-plugin-tts (the version of Vilic Vane is discontinued).
- Change the plugin to reference other cordova plugin (for example https://github.com/spasma/cordova-plugin-tts-advanced/) and make little changes in plugin.
- Search other speech plugin. :-(
- Download https://github.com/LuisMAlmeida/cordova-plugin-tts, make changes in code, generate the .zip and reference it in the plugin (https://success.outsystems.com/Documentation/10/Extensibility_and_Integration/Mobile_Plugins/Using_Cordova_Plugins#Referencing_Cordova_Plugins).
The best option is 1 but perhaps the team of this plugin can give you more information.
Kind regards, David.