The European Court of Human Rights has ruled that an application over the long-running so-called "gay cake" case is inadmissible.
The court has said that the decision is final.
In 2018, the UK Supreme Court ruled that Northern Ireland gay rights activist Gareth Lee was not discriminated against when the Christian owners of a Belfast bakery refused to make him a cake iced with the slogan "Support Gay Marriage".
Mr Lee then referred the case to the ECHR, claiming that the Supreme Court failed to give appropriate weight to him under the European Convention of Human Rights.
Mr Lee claimed that his rights were interfered with by the decision of the UK's highest court to dismiss his claim for breach of statutory duty to provide services, and the interference was not proportionate.
However the seven-judge chamber of the ECHR said that in order for a complaint to be admissible, "the Convention arguments must be raised explicitly or in substance before the domestic authorities."
The court said Mr Lee had not invoked his Convention rights at any point in the domestic proceedings.
"By relying solely on domestic law, the applicant had deprived the domestic courts of the opportunity to address any Convention issues raised, instead asking the Court to usurp the role of the domestic courts," the ECHR ruling said.
"Because he had failed to exhaust domestic remedies, the application was inadmissible."
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In a statement, Mr Lee said he had "very much hoped for a different outcome" from the ECHR application.
He said he was "most frustrated that the core issues did not get fairly analysed and adjudicated upon because of a technicality."
Ciaran Moynagh of Phoenix Law, who brought the case to the ECHR, said they will "now consider whether a fresh domestic case is progressed".
Mr Moynagh added that the "substantive issues" raised by Mr Lee remain unaddressed.
The controversy first flared when Mr Lee, a member of the LGBT advocacy group QueerSpace, ordered a £36.50 cake in May 2014 featuring Sesame Street puppets Bert and Ernie for a private function marking International Day Against Homophobia from Ashers bakery in Belfast.
His order was accepted and he paid in full, but, two days later, the Christian owners of the company called to say it could not proceed due to the message requested.
Mr Lee then launched the legal case, supported by Northern Ireland's Equality Commission, alleging discrimination on the grounds of his sexuality, and won hearings at the county court and the Northern Ireland Court of Appeal in 2015 and 2016.
But the owners of Ashers, Daniel and Amy McArthur - backed by the Christian Institute - challenged those rulings at the Supreme Court, and in 2018 five justices unanimously ruled that they had not discriminated against the customer.
The court's then president said the McArthur family hold the religious belief that "the only form of marriage consistent with the Bible and acceptable to God is between a man and a woman".
She said: "As to Mr Lee's claim based on sexual discrimination, the bakers did not refuse to fulfil his order because of his sexual orientation.
"They would have refused to make such a cake for any customer, irrespective of their sexual orientation.
"Their objection was to the message on the cake, not to the personal characteristics of Mr Lee or of anyone else with whom he was associated."
Mr Lee said at the time that the refusal to make the cake made him feel like a "second-class citizen".
The McArthurs said they did not turn down this order because of the person who made it, but because of the message requested on the cake.
