It is a variant of 'ABC', which in this context should be read as a primer, or first book for teaching children their letters.
Searching the OED brings up the definition for ABC, and includes 'Apcie', along with other variant spellings, in the entry. I searched Google for 'Apcie' together with "ABC" and found the 'History of the Horn Book. Volume 2' which contains:
In early days before the invention of printing, the primer, or little collection of devotions used in schools, opened with the criss-cross-row or alphabet arranged in horn-book fashion, and the terms “ prymer ” and “ABC ”—the Middle English name for the alphabet—naturally came later to be applied to all elementary books for children’s use. The teacher of religion and of the alphabet went always together, and some account of the early MSS. and books of instruction is almost necessary in a History of the Horn-Book. Copies of the primer (the earliest known is about 1400 A.D.) are scarce, but considering the efforts made to destroy them, the wonder is that so many have been preserved. Cut 166 shows the first page, slightly reduced, of a vellum MS., a fourteenth-century common prayer-book in English, now in the Glasgow Hunterian Library. The contents are of the usual order—The Hours, The Seven Psalms, The Fifteen Psalms, The Litany, The Office for the Dead, and The Commenda tions—with some additions before and after the usual text.
ABC was written in numerous forms—abc, a b c, apece, apecy, apcie,
apsie, absee, absie, absey, abeesee, abce, abcy, abece, abice, abicee,
abcie, abcee, a-bee-cee, a-pece, apecey ; in Welsh Yr Abiec. The
earliest reference given in the (Oxford) New English Dictionary
relating to the use of one of the forms (abece) is 1297. Cotgrave
gives “Abece, Abcee, the Cross-row, an Alphabet.”
A hornbook being:
book that serves as primer for study. The hornbook originated in
England as long ago as 1450,1 or earlier.2 The term has been
applied to a few different study materials in different fields. In
children's education, in the years before modern educational materials
were used, it referred to a leaf or page displaying the alphabet,
religious materials, etc., covered with a transparent sheet of horn
(or mica) and attached to a frame provided with a handle.