...
In general your request should have form https://ochem.eu/modelservice/getPrediction.do?modelId=MODEL_ID&mol=MOLECULE where MODEL_ID is the public model identifier and MOLECULE is the analyzed molecule.
The YOUR_The MOLECULE can be in SMILES or SD format. For both the formats, multiple molecules can be posted using $$$$ separator.
It is much more efficient to predict molecules in batches rather than posting separate tasks for each molecule.
...