Sourdough starter outside of bread making (bika ambon)

hi! I am currently making Bika Ambon, a traditional Indonesian cake which usually uses commercial yeast to achieve the beautiful strands shown in the picture. I wanted to make a sourdough version and after searching, one source said that 100 gr of sourdough is enough to substitute 5-7 gr of yeast. Now, the recipe for the bika ambon itself is as follow:

Normal recipe:

• 200 ml coconut milk

•  

• Raising agent:

• 25 gr all purpose flour

• 1 tbsp sugar

• 60 ml water

• 4 g instant yeast

•  

• Main ingredients

• 1 whole egg

• 4 egg yolk

• 50 g tapioca flour

• 100 g sugar

method:

1. Mix all of the raising agent and let sit until the yeast is frothy and bubbly

2. bring the coconut milk to a boil 

3. mix the egg, yolk and sugar until thick, add in the tapioca flour

4. add in the yeast, fold in the coconut milk

5. cover for 2 hours or until double in size

6. bake in a 180 C oven for 45 minutes

Now for the sourdough version, i have substituted the raising agent for 80 gr of sourdough starter, and let it sit for almost 5 hours now, but there is no sign of it rising whatsoever. the only difference that i can notice is a slight yeasty smell and frothiness forming on top of my mixture. Note that it is a liquidy mixture and not a dough in any form. I know that maybe none of the readers have ever made Bika Ambon before but maybe by judging the ingredients, are there any factors that could inhibit fermentation from sourdough starter? Note that my sourdough starter is 1 month old, with a (1:1:1 sourdough:hard flour:water). Am i using too little of souirdough? is the presence of egg too much so that it inhibits the fermentation? Will this ever work using a sourdough?? any insights will be very much appreciated