Place 6 clean 125ml mason jars on a rack in a boiling water canner, cover jars with water and heat to a simmer. Set screw bands aside. Heat snap lid sealing discs in hot water, not boiling. Keep jars and sealing discs hot until nearly ready to use.
With scissors or knife, cut apricots into 1/8 inch slices. Measure into a large deep stainless steel saucepan with vinegar; let stand 4 hours. Add diced red onion and green peppers to to apricots. Stir in sugar.
Over high heat, bring mixture to a full rolling boil that cannot be stirred down. Add liquid pectin squeezing entire contents from pouch. Boil hard for 1 minute, stirring constantly. Remove from heat and quickly skim off foam, if necessary.
Quickly pour jelly into a hot jar, dividing solids equally among jars and filling to within 1/4 inch of top of the jar headspace. Wipe jar rim removing any food residue. Center hot sealing disc on clean jar rim. Screw band down tight until resistance is met, then increase to fingertip tightness. Return filled jar to rack in canner. Repeat for remaining jelly.